Medical devices for placement in a human or other animal body are well known in the art. One class of medical devices comprises endoluminal devices such as stents, stent-grafts, filters, coils, occlusion baskets, valves, and the like. A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit through a body lumen in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside and/or outside thereof. A covered stent is commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), a stent-graft, or endograft.
An endograft may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an endograft is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the endograft, typically restrained in a radially compressed configuration by a sheath, crocheted or knit web, or catheter, is delivered by a stent delivery system or “introducer” to the site where it is required. The introducer may enter the body from an access location outside the body, such as through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. The term “proximal” as used herein refers to portions of the stent or delivery system relatively closer to the end outside of the body, whereas the term “distal” is used to refer to portions relatively closer to the end inside the body.
After the introducer is advanced into the body lumen to the endograft deployment location, the introducer is manipulated to cause the endograft to be deployed from its constrained configuration, whereupon the stent is expanded to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion is typically effected by spring elasticity, balloon expansion, and/or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Among the many applications for endografts is that of deployment in lumen for repair of an aneurysm, such as an abdominal aortic aneurysm (AAA). An AAA is an area of increased aortic diameter that generally extends from just below the renal arteries to the aortic bifurcation. AAA generally results from deterioration of the arterial wall, causing a decrease in the structural and elastic properties of the artery. In addition to a loss of elasticity, this deterioration also causes a slow and continuous dilation of the lumen.
The standard surgical repair of AAA is an extensive and invasive procedure typically requiring a weeklong hospital stay and an extended recovery period. To avoid the complications of the surgical procedure, practitioners commonly resort to a minimally invasive procedure using endoluminal endograft to reinforce the weakened vessel wall, as mentioned above. At the site of the aneurysm, the practitioner deploys the endograft, anchoring it above and below the aneurysm to relatively healthy tissue. The anchored endograft diverts blood flow away from the weakened arterial wall, minimizing the exposure of the aneurysm to high pressure.
Intraluminal stents for repairing a damaged or diseased artery or to be used in conjunction with a graft for delivery to an area of a body lumen that has been weakened by disease or damaged, such as an aneurysm of the abdominal aorta, are well established in the art of medical science. Intraluminal stents having barbs, hooks, or other affixation means to secure the stents to the wall of the lumen in which they are to be deployed are also well known in the art. Referring now to FIG. 1, there is shown an exemplary embodiment of an endograft 10 comprising a stent 11 having a graft lining 12 and a plurality of hooks 13 for affixation to the wall 14 of aorta 15 afflicted with an aneurysm. The affixation means, such as hooks 13, are important because subsequent movement (or “migration”) of the endograft may cause the aneurysm to become exposed to blood pressure. In particular, if the device migrates proximally over time in the direction of arrow A, as shown in FIG. 1, a leak at distal end 16 of the device, sometimes referred to in the art as a “Type I endoleak,” may cause blood to flow undesirably to the aneurysm.
Even with standard affixation means, however, continued progression of the aneurysm may lead to diametric expansion of the aneurysm along arrows B as shown in FIG. 1. In particular, in AAA applications, the portion of the aneurysm closest to the renal arteries 17, referred to herein as the “renal neck” 18, may undergo this diametric expansion. The “renal neck” is often referred to by practitioners as the “proximal neck” where the term “proximal” means anatomically as closer to the heart.
Because this application does not use anatomical definitions of “proximal” and “distal,” the term “renal neck” is used herein avoid confusion. This diametric expansion of the renal neck may result in ineffective engagement of one or more of the hooks around the circumference of the renal neck, and may lead to a Type I endoleak, as illustrated by separation 20 between aorta wall 14 and endograft 10 in FIG. 2, and/or distal migration of the endograft.
Accordingly, it can be seen that while the art has advanced the use of barbs to minimize migration of a deployed stent-graft, even the use of such barbs may not be sufficient to prevent endoleaks. Accordingly, there is still a need in the art for endograft designs having enhanced affixation characteristics.